Ampeg SVT 4 Pro Board Layout diagram

[oc disorder]

Hi After replacing 10 mosfets a couple of Mj350'S ,10 x 5 watt resistors
and lost count of the fusable resistors... its still drawing way too much current on turn on (globe in series) so have to pull apart again....
Hopeing it might be obvious like bridge rectifier (which I forgot to check).
Had a charcoal section !!! where I had to repair tracks so may also have got that wrong hence the request for a layout diagram.
Seemed to me only one side had gone so also looking for points to test the power amps separately by alternately removing the supply to them.
Any help appreciated ...

[Twist]

This is version "D". Also check all small signal diodes and zeners on that side. I've rebuilt a few of those and I seldom find every bad component the first time. I've come to use the shotgun approach on those and replace everything.

[oc disorder]

Thanks for that Twist.
It seems its not so easy to individually test the channels.
The two 10v zeners were gone and two of the 200v 0.1amp diodes also.
I couldn't get hold of 1N3070's so substituted 1SS82 which are a fast recovery 250v 0.2amp diode.I did notice that the voltage drop across them was slightly more than the 3070's but thought it insignificant.
I have noticed that both sides are presenting about 7 volts dc at the output
with a 200watt light bulb in series with the mains which is about 114v (less than half the 240v pwr here).
The rectifier is putting out about +/- 38volts so as I couldnt find any faults passively with the second channel I am wondering if it is ok and just can't turn on and stabilize without the full supply.
I'm hesitant to turn it on with full power 'cause of the destruction that can occur if I've missed something.I pulled the pre-amp tubes to try to reduce
the turn on consumption but didn't seem to make any difference.
Like taking a flea from an elephant to reduce its weight !
Suppose I'll have to apply power at some stage... Its not easy to work on !

[Twist]

I forgot to mention sometimes the solder joints on the main bridge rectifier crack. The last one I had come into the shop had fried one channel but I also found D4 and C3 were faulty. Have you also replaced the MPSA56 and MPSA06 transistors? Anyway this particular amp was working fine when I sent it out and about a week later the customer called me and said the same channel had gone out again. I was sick because I was going to have to eat the cost of rebuilding it again.
Sure enough the channel was dead but all the components were fine. It turned out that there was a tiny piece of metal inside the sealed speaker relay for that channel. When the relay was acctuated the metal stuck to the something inside the relay and wouldn't complete the circuit. This guy runs the amp bridged all the time and I wondered if somehow this may have caused the damage from the beginning or could have just been two separate issues. He has been playing it for several months now with no problems. I wrote down all the components I replaced on the last one and could post it for you if it would help. It's hand written and would have to be scanned.

[Mars Amp Repair]

yes these are a bear to work on. You can set them up to run safely without putting them back into the box everytime. Nutz! I didn't keep the pix I took of the amp in the service position :-\

Anyway, I also have seen where the small bias feedback transistors that are clamped to the heatsink develop bad solder connections, but it looks like your repair is waaay beyond that point.

I've also had bad connections on the regulator transistors on that little piggyback board mounted on the rear of the main heatsink causing offset. These things can really be a bear.
glen